FPGA Game Boy Emulator

This repository contains a Game Boy / Game Boy Color emulator, written in Chisel, that can be run on an FPGA. Read the full writeup here.

Currently, only the Pynq-Z2 is supported, although the core of the emulator should be able to be used on any FPGA with sufficient resources.

Building

A precompiled bitstream is available under Releases.

Setup

Install Vivado

Currently this project uses Vivado 2020.2. The free edition is sufficient. Make sure to install with support for Zynq-7000 SoCs.

Install the Pynq-Z2 Vivado board files.

Additionally, you should set up a shared IP cache to speed up synthesis of Xilinx IP:

1. Create the ~/vivado_ip_cache directory (could be located somewhere else).
2. Create the file ~/.Xilinx/Vivado/Vivado_init.tcl
3. In that file, add set_param project.defaultIPCacheSetting /home/eli/vivado_ip_cache/ (substituting the absolute path to the IP cache directory).

Install other tools

You'll need to install JDK 8 or later, and Scala Build Tool (sbt). Additionally, install FuseSoC.

Building the bitstream

From the top-level directory:

fusesoc --cores-root . run --build --target=pynq_z2 elipsitz:gameboy:gameboy

This will generate a .bit and .hwh file, which need to be accessible to the PS Python code.

Running

Setup

Install Pynq Linux on the Pynq-Z2, and install the pip packages listed in python/requirements.txt.

Transfer the gameboy_ps Python module (located in the python directory) to the Pynq-Z2.

Place the gameboy.bit and gameboy.hwh files from the build process in the gameboy_ps/resources directory.

HDMI and Controller

Connect an HDMI cable from the "HDMI OUT" port on the Pynq-Z2 to a monitor or TV.

Attach an Xbox-compatible controller to the USB port of the Pynq-Z2.

Running

As root, run python3 -m gameboy_ps <path to ROM directory>, passing the path to the directory containing ROM files.

The program will load the bitstream to the PL. It takes a few seconds to load all of the Pynq libraries, but the main menu should soon show up on the display.

Warning: the audio output can be quite loud. Start at the lowest setting on the monitor/TV and increase it as needed.

Building the cartridge adapter board

To play physical cartridges, you'll need to assemble the adapter board. KiCad board files can be found in the pcb/pynq_adapter_rev2 directory. The schematic is pre-populated with LCSC part numbers for easy assembly at JLCPCB.

You'll need to add a few components yourself. These are all easy to solder:

• A 2x20 0.1mm female pin header (e.g. this one). These are used for Raspberry Pi HATs, so they're pretty easy to find.
• A SPDT slide switch such as the EG1218, or just a 1x3 strip of 0.1mm male pin header and a jumper.
• A GBA SP slot (such as this one). These can be found quite cheaply on eBay or Aliexpress as well. They're all pretty much the same.
• If desired, a GBA link port (e.g. this one). These can also be found easily from other sources.

The other parts are relatively small, so I don't recommend hand soldering the board. However, if you want to assemble the whole thing yourself, in addition to assorted resistors and capacitors, you'll also need:

• 6x 74LVC1T45DCK 1-bit level shifters.
• 2x 74LVCH16T245DGGR 16-bit level shifters. The non 'H' version should work as well, but the 'H' (bus hold) version is preferable.

Appendix

Getting Xbox controller to work on Pynq-Z2

This needs the xpad and joydev drivers. Pynq Linux isn't built with them. If you're running Pynq Linux with kernel 5.15.19-xilinx-v2022.1, prebuilt kernel modules can be found in the extra directory in the repository. Otherwise, to build loadable kernel modules from scratch:

On the Pynq-Z2, go to /lib/modules/5.15.19-xilinx-v2022.1/build.

Download the right version of xpad.c to drivers/input/joystick/xpad.c.

And do the same with joydev.c, to drivers/input/joydev.c.

The build commands in /lib/modules need to run with sudo due to permissions issues.

Do sudo make menuconfig and set:

• Device Drivers --> Input device support --> Joystick interface to M (for 'module')
• Device Drivers --> Input device support --> Joysticks/gamepads --> X-box Gamepad support to M (for 'module')

Save and exit.

Then build the modules:

sudo make scripts
sudo make distclean
sudo make prepare
sudo make modules_prepare

sudo make -C . M=drivers/input/ joydev.ko
sudo make -C . M=drivers/input/joystick xpad.ko

Install the modules so that they'll be loaded automatically on boot. Copy the .ko files to /usr/lib/modules/$(uname -r)/kernel/, and append to /etc/modules:

joydev
xpad

Alternatively, use insmod <modules>.ko to load them once.

Make sure the xilinx user is in the group input: sudo usermod -a -G input xilinx (and re-login)

Install the Python library with sudo pip3 install xbox360controller

Create the device nodes if needed: https://docs.kernel.org/input/joydev/joystick.html#device-nodes

cd /dev
rm js*
mkdir input
mknod input/js0 c 13 0
mknod input/js1 c 13 1
mknod input/js2 c 13 2
mknod input/js3 c 13 3
ln -s input/js0 js0
ln -s input/js1 js1
ln -s input/js2 js2
ln -s input/js3 js3